Fin Unit with Elastic Attachment System on an Underside of a Marine Apparatus

ABSTRACT

The invention relates to a fin unit ( 2 ) with elastic attachment system on an underside ( 1 ) of a marine apparatus, such as a wind surf, kite surf, fly surf, wakeboard, knee board and particularly a surfboard. The fin in the mounting thereof is partially made to self-align in the flow of liquid medium with the aim of avoiding the hydrodynamic stall caused by the passage of high turbulence and/or large lateral movements caused by the surfer in extreme motion. The possibility for self-orientation is due to three fundamental parameters which are: the type of elasticity of the attachment system ( 3 - 4 - 5 - 27 ), the forward position of the centre of gravity G towards the leading edge ( 15 ) and the form of the root profile ( 9 ) of the fin ( 2 ) which has a thickening ( 7 ) of the trailing edge thereof.

The present invention relates to a fin unit with elastic attachment system on the underside of a marine apparatus, such as a windsurf board, kite surf, fly surf, wake board, kneeboard and particularly a surfboard.

Surfboards are usually equipped with one or with several fins, more commonly three, fixed at the tail of the board, on the careen (lower surface of the board). Two methods of fixture exist, one consists in bonding the fins on the board to make them interdependent, the other consists in having removable and interchangeable fins via a box or an insert of fixture incorporated in the board.

The traditional fins are generally manufactured using a plate made up of a multitude of fiberglass layers and resin, machined or shaped by hand. Then they are made interdependent with the board by bonding with fiberglass fabrics, unidirectional fiber and resin.

This mode of fixture makes it possible to establish at the root a peripheral fillet to improve the hydrodynamic characteristics at the base of the fins.

On the other hand, the presence of fixed fins on the board during the stages of completion of manufacture involves an increased duration of this operation and thus the cost of labor, as well as an increase in the weight and a reduction of the quality of the board finish surrounding the fins position.

For these ten last years, many companies launched themselves in the manufacturing of removable fins systems because they have multiple advantages, on one hand for surfers whom according to the type of sport use several type of fins with the same board. On the other hand, for the board manufacturers who are seeking for speed of installation of the fins and a less cumbersome and an easier storage of the boards in the warehouse or during transportation.

The boards are most commonly equipped with fins made of thermoplastic material reinforced with glass powder. They are heavy and present weak mechanical properties compared with those traditional fins when they are submitted to a bending stress.

To obtain the best performances in the wave, during the various stages of manufacture of a board, the shaper pays a very detailed attention to the distribution of volume and on its balance compared to its widest point.

Despite everything, when the board is equipped with its fins, the weight of those induces a shift backwards of the centre of gravity compared to the required optimal position.

Moreover, disappearance of the fillet, represented by an amount of resin at the base of the fin, reduces the hydrodynamic performances while generating in certain configurations an inopportune stall of the fluid and a loss of control of the board by the surfer.

Generally the fins are maintained in position on the board by a system including one or more screws which fix them in place in the inserts, as described in the patent FR 2 691 943. That forces the surfer to use a specific toll in order to mount/dismount the fins, representing certain difficulties when being on a beach.

On certain marketed systems, a frequent assembly/disassembly of the fin or a too high tightening torque of the screw can damage the threading in the plastic insert, and even deteriorate the hexagonal head of the screw. This dysfunction can involve a fin loss or an impossibility of assembling/disassembling it from the board.

Others disadvantages have been identified on the existing systems, such as the possibility of perforating the board fiber reinforcement during the fin assembly/disassembly because of a front/back swing of this one. As well as the importance of board repair after insert's tear off in the case of violent impact, the shape and the weight of the used insert of fixture and its mode of embedding in the board.

Moreover the stiffness of fin/board assembly mounting causes, in extreme configuration of the evolution practiced by the surfer, the formation of vortex and vibrations.

The purpose of the invention is to facilitate the control of the board by a surfer by having removable fins whose constitution, shape and assembly on the board, allow to obtain on one hand, an improvement of the hydrodynamic efficiency by reducing the formation of vortex/vibrations and on the other hand, to increase the range of evolution in the waves in a marine environment.

Thanks to the invention, this goal is reached while making the fin semi articulated or partially self directional in its fluid environment evolution, in order to push back the hydrodynamic stall caused by the crossing of high turbulences and/or by the strong lateral movements applied by the surfer in extreme motion, thanks to an elastic means of fastening combined with the forward position of the centre of gravity G toward the leading edge and the shape of the root profile of the fin.

The fin unit with elastic attachment system, in accordance with the invention, presents a certain number of advantages. Given that the fin is mounted semi articulated on the board, in addition that it improves the hydrodynamic performances, it improve also the service life of the whole assembly with respect to mechanical shocks or hydrodynamic fluctuations, which are amortised by the elastic attachment system.

The invention is described hereafter using examples and references to joined illustrations, in which:

FIG. 1 is a side plan view representing the principal components between fins and careens.

FIG. 2 is a cross sectional view of drawing 1 showing the shape of the tenon profile and the insert.

FIG. 3 illustrates the fin in its work configuration in the fluid with its associated turbulent flows.

FIG. 4 is a bottom plan view of the board equipped with three fins.

FIG. 5 is a rear view of the board.

FIG. 6 is a perspective view of the fin/insert assembly.

FIG. 7 is a rear view of the fin considering the trailing edge.

FIG. 8 illustrates different shapes and surface conditions of tenons.

FIG. 9 is a perspective view of the insert embedded in the board.

FIG. 10 cross sectional view of the insert including its angular jig fitted in the board.

FIG. 1 illustrates the whole assembly of the fin (2) on the careen (1). The fin is equipped with at least one tenon (3) which is introduced into an insert (5) bonded to the careen (1) including an elastic matter (4) coating if necessary a sleeve (27) in order to hold and lock the tenon after its insertion in the housing.

The mechanical unit thus defined represents the said elastic means of fastening (3-4-5-27). They bring a partial mobility of the fin around OZ axis with yawning moment Mz and around OX axis with rolling moment Mx.

FIG. 2 represent, according to a cross sectional top view, the shape of the insert (5), the shape of the tenon (3) and the shape of the root profile (9) of the fin (2).

The root profile includes a thickening (7) of the trailing edge (8) of a value equal or lower than the maximum cross section thickness situated at approximately 25% of the airfoil cord. This thickening (7) is built on a height H of value at least equal to that of the maximum cross section Mc.

The fin equipped with tenon (3) is manufactured in such a way that it can float in water. It is composed by a profiled core (16) made of very light material covered with a skin (17) of great strength with a leading edge (15) reinforcement by successive layers. According to the needs, the fin will be fitted with a ballast (6) for two essential reasons. Namely, the first; in order to position the fin centre of gravity G close to the root (9) and in front of OZ axis, the second; as to adjust the Eigen frequencies Hx and Hz around OX and OZ axis.

FIG. 3, as a whole, makes it possible to explain how the fin (2) reacts when it is submitted to more or less laminar and fluctuating flows. Indeed, for a given speed V and an angle of incidence i the fin is subjected to a lift P and a drag T whose centre of action O′ is located at the back of OY fastener axis.

For an angle of incidence close to stall we observe an amplification of marginal tip vortex t_(m), an amplification of root turbulences t_(e) and of vibrations.

These last can be rather destructive when are close to the natural frequencies HP of the assembly in a turbulent fluid environment.

These disadvantages are pushed back while making the fin reactive and partially self directional while exploiting three fundamental parameters. To know;

-   -   The elastic means of fastening (3-4-5-27), which according to         the grade of elasticity, determines the importance of the         angular displacement Δi and Δj around OX-OY axis. Thus a strong         variation of lift ΔP, caused by a strong variation of speed ΔV,         swirl or gust, will be limited by the rotation of the fin in the         way of angle of attack reduction by considering that action         centre O′ is located at the rear of OZ axis.     -   The form of the root (9) profile of the fin, whose trailing edge         (8) includes a thickening (7) as shown in FIGS. 1 and 2.

At a strong variation of lift ΔP, this shape limits the stall due to the imperfections of fin/careens surfaces junction and thus limit the displacement of the action centre towards the leading edge of the fin.

-   -   The position of the centre of gravity G that will be generally         adjusted via a ballast (6) so that the inertial forces bring         back to OX and OY axis generate, during the acceleration of         speed ΔV, a rotation of the fin in the way of incidence         reduction.

It is under these conditions that we can say that the fin, in the case of in extreme motion or important variations of speed ΔV at great incidence, is self adjustable in incidence by the fact that the tenon (3)/insert (5) linkage is elastic and that inertial forces, applied at the centre of gravity G and that the hydrodynamic forces applied to the action centre O′, induce yawning moments Mz and rolling moments MX which reduce the gust effect by the angular variations Δi and Δj. The tenon (3), according to the mountings, can be of circular section or rectangular or more or less of elliptic section as on the FIG. 2.

It can contain at its end a notch or a throttling (10) as to self position it in its sleeve (27) during its insertion and to be locked in at its end of travel on an elastic strip (28) or a spring ring of circlips (20) type. The disassembly of the fin operates by pulling it along OZ axis while pushing on a located point on the insert as to disengage the elastic strip or the pin from the tenon notch.

The fin, in another type of achievement can be locked in position by a cord (11) fixed at the tenon end or on the root (9) of the fin. This cord crosses through the thickness of the board in order to be fixed and tended by a rubber band (12) located and fixed (13) in a slot (14) practiced in the deck of the board.

The FIG. 6 represents another type of achievement according to which the fin (2) is attached to the careen (1) by two tenons (3 a-3 b) inserted in two mortises (19 a-19 b) of a non elastic material. Each mortise include inside one or more elastic matter rings (18 a-18 b) in such a way that the tenons once introduced are maintained by the radial pressure of the rings which allow however a light elastic displacement of the fin (around OX and OZ axis) in the gap left between the diameter of the tenons and that of the mortises.

The OZ axis position is between the axis of the tenons (3 a-3 b). But in the case where we want to adjust OZ axis as close as possible to the tenon (3 a) axis, it is enough to use rings with different elastic deformation under the same effort. It is the case in our assembly where the rings (18 a) have a smaller modulus of elasticity, that is to say harder than the rings (18 b). A difference of size or shape of the ring contained in the mortises (19) before and back can produce the same effect with an identical modulus of elasticity.

FIG. 8 represents the use of various tenons. The tenon is a part brought back during the manufacture of the fin (2) whose material used is either a metal stainless or titanium, or a composite. The tenon has outside a smooth or ridged or knurled surface to strengthen the behavior of the assembly with the rings (18 a-18 b) and inside a tubular cavity (22) where there is a flexible bond (23) of safety connecting one and the other of the two ends (24-25) of the tenon which in the event of rupture makes it possible to not lose the fin in the fluid environment.

The FIG. 9 represents the insert (5) assembled in the board. It is a kind of very hard material cage including outside protruding parts (26) for the mooring and the bonding in the careen (1). Inside the insert other protruding parts (29) are arranged to receive equipments allowing the coupling with at least a tenon (3).

This assembly, to ensure cost savings by reducing the duration and facilitating the installation of this one in the board, includes, FIG. 10, an angular positioning jig (30) composed of three arms (31-32 a-32 b) each one provided with a pin (33). The arm (31) of length greater than that of the arms (32 a-32 b) is provided with at least a divisible pin (34) dimensioned and specified with the angle (ψ) required.

This angle (ψ) is defined by the designer for the angular positioning of the lateral fins, it defines its angular position of origin.

Each ignition pin (34) represents an angular increment (Δψ) comprised between 0.25° and 1°, with regard to the precedent. During the lateral fins installation the designer must break one or more pins (34) in order to obtain the angle that he wishes to set for the fin, given by the plane support of the pin (34) and the pins (33).

With regard to the installation of the central fin, it is necessary to break all the pins (34) to obtain an angle of 0°, given by the plane support generated by the three pins (33).

In order to maintain the contact between the three pins and the careen surface, the use of a weight on the insert can be necessary during its installation by bonding in the board.

Once the inserts are interdependent to the board with the sought angle, a final grinding is carried out to level the insert with the careen of the board in order to eliminate all the protruding members, represented in the hatched part (35) on FIG. 10.

In the case where the external surface of the equipped insert does not align itself exactly with that of the careen (1) or presents asperities, the clearances or the gaps between fin and careen will be filled by an elastic joint (21) bonded on the careen or at the base of the fin. 

1. Removable fin unit with system of fastener on careen of a marine apparatus (1) such as surfboard, kite surfing, fly surfing, wake board, knee board, windsurf board or similar, characterised by the fact that the fin (2) is partially made self directional in its evolution in fluid environment in order to push back the hydrodynamic stall caused by the crossing of large turbulences and/or the strong lateral movements applied by the surfer in extreme motion, thanks to elastic means of fastening (3-4-5-27) combined with the forward position of the centre of gravity G and the form of the profile (7) out of root (9) of the fin (2).
 2. Fin unit according to claim 1, characterised in that the form of the profile of the fin (2) out of root (9) includes a thickening (7) of the trailing edge (8) of a value equal or lower than the maximum cross section thickness situated at approximately 25% of the airfoil cord, the said thickening being built on a height H of value at least equal to that of the said maximum cross section.
 3. Fin unit according to claim 1, characterised in that the means of fastening units are represented by an insert (5) embedded in the careen (1) including an elastic matter (4) coating a sleeve (27) in order to hold at least a tenon (3) out of root (9) of the fin (2), which assembly allows a partial elastic mobility of the fin around OZ axis and OX axis.
 4. Fin unit according to claim 1, characterised in that the fin (2) assembled with its means of fastening (3-4-5-27) is brought as to be able to have angular displacement (Ai and Aj), in the case of over lift pressure of hydrodynamic nature ΔP, around vertical axis OZ in yawning Mz and around longitudinal axis OX in rolling Mx.
 5. Fin unit according to claim 1, characterised in that the fin (2) equipped with tenon (3) is manufactured in such a way that it can float in the water, that is to say it is composed by a profiled core (16) made of very light material covered with a skin (17) of great strength with a leading edge (15) reinforcement by successive layers, which includes according to the needs a ballast (6) to adjust the natural frequencies HP, to position the centre of gravity (G) of the fin close to the root (9) and in front of OZ axis.
 6. Fin unit according to claim 1, characterised in that the fin (2), in the case of extreme motion or important variations of speed ΔV at great incidence i, swirl or gust, induce strong variation of lift ΔP, is self adjustable in incidence by the fact that the tenon (3)/insert (5) linkage is elastic and that inertial forces, applied at the centre of gravity G and that the hydrodynamic forces applied to the action centre O′, depending on the swirling effect from induced drag t_(m) and root turbulence t_(e), induce yawning moments Mz and rolling moments Mx which reduce the gust effect by the angular variations Ai and Aj.
 7. Fin unit according to claim 3, characterised in that the tenon (3) is of circular section or rectangular or more or less elliptic, it can contain at its end a notch or a throttling (10) as to self position it in its sleeve (27) during its insertion and to be locked in at its end of travel on an elastic strip (28) or a spring ring of circlips type (20).
 8. Fin unit according to claim 7, characterised in that the fin (2) is locked in position by a cord (11) fixed at the tenon end or on the root (9) of the fin, which cord crosses through the thickness of the board in order to be fixed and tended by a rubber band (12) located and fixed (13) in a slot (14) practised in the deck of the board.
 9. Fin unit according to claim 7, characterised in that the fin (2) is attached to the careen (1) by two tenons (3 a-3 b) inserted in two mortises (19 a-19 b) of a non elastic material, each mortise include inside one or more elastic matter rings (18 a-18 b) in such a way that the tenons once introduced are maintained by radial pressure, at the level of the throttling (10), which allow however a light elastic displacement of the fin (around axes OX and OZ) in the gap left between the diameter of the tenons and that of the mortises.
 10. Fin unit according to claim 9, characterised in that the ring (18 a) and the ring (18 b) present different elastic deformations under the same effort, due to the difference of modulus of elasticity of chosen elastomer and/or with the difference of the shape of the ring as to position the OZ axis as closer to the front tenon axis.
 11. Fin unit according to claim 9, characterised in that the tenon (3 a-3 b) is a part brought back during the manufacture of the fin (2) whose material used is either metal stainless or titanium, or a composite, this same tenon includes outside a smooth or ridged or knurled surface to strengthen the behaviour of the assembly with the rings (18 a-18 b) and inside a tubular cavity (22) where there is a flexible bond (23) of safety connecting one and the other of the two ends (24-25) of the tenon which in the event of rupture makes it possible not to lose the fin in the fluid environment.
 12. Fin unit according to claim 3, characterised in that the insert (5) is a kind of very hard composite material cage including outside the protruding parts (26) for the mooring and the bonding in the careen (1) and inside other protruding parts (29) to receive equipments allowing the coupling with at least a tenon (3), the said insert (5) as to facilitate its installation in the board includes an angular positioning jig (30) composed of three arms (31-32 a-32 b) each one provided with pin (33), the said arm (31) of length greater than that of arms (32 a-32 b) is provided with at least a detachable pin (34) dimensioned and specified with the angle (ψ) required.
 13. Fin unit according to claim 2, characterised in that the fin includes at its root (9) an elastic joint (21) filling the clearances or the gaps between fin and careen. 